Quan Chen

A magnetic resonance study of pore filling processes during spontaneous imbibition in Berea sandstone

A new magnetic resonance technique, DDIF (the decay of magnetization due to diffusion in the internal field), was combined with mercury porosimetry to investigate pore geometry, including pore- and throat-size distribution, and pore connectivity for porous media. A comparison of DDIF spectra for a fully water saturated Berea sandstone, with the partially saturated sample by centrifugation in air, indicated that DDIF can be used for the measurement of water filled pore size distribution in partially saturated porous media. Dynamic water imbibition into air-filled Berea sandstone was studied using the DDIF technique. Simultaneously, in situ three-dimensional saturation and capillary driven water penetration were monitored using Conical-SPRITE, which is a rapid, centric scanning, spin-density weighted single point three-dimensional magnetic resonance imaging technique. These measurements provide direct evidence for differences in the pore filling mechanisms for co-current imbibition and counter-current imbibition in Berea sandstone. During co-current imbibition, water flows through the pores and connected throats with a piston-type mechanism. Air is displaced from the sample by the leading edge of the waterfront, resulting in a macroscopic piston-like flow through the entire sample. During counter-current imbibition, water flows through the pores and connected throats with a film-like structure along the corners and surfaces of the pore space. Air escapes from the sample by flowing through the center of the pores and pore throats, in the opposite direction. Once the penetrating waterfronts meet, at the sample center, there is a global, uniform increase in water content.

Flow imaging of fluids in porous media by magnetization prepared centric-scan SPRITE

MRI has considerable potential as a non-destructive probe of porous media, permitting rapid quantification of local fluid content and the possibility of local flow visualization and quantification. In this work we explore a general approach to flow velocity measurement in porous media by combining Cotts pulsed field gradient flow encoding with SPRITE MRI. This technique permits facile and accurate flow and dispersion coefficient mapping of fluids in porous media. This new approach has proven to be robust in characterizing fluid behavior. This method is illustrated through measurements of flow in pipes, flow in sand packs and flow in porous reservoir rocks. Spatially resolved flow maps and local fluid velocity distribution were acquired.

Quantitative magnetic resonance imaging methods for core analysis

Abstract The majority of sedimentary rocks have significant paramagnetic impurities, which lead to magnetic resonance signal lifetimes too short to be detected by clinical magnetic resonance imaging (MRI) methods. Quantitative information is the ultimate goal for rock-core analysis. The SPRITE (single-point ramped imaging with T1 enhancement) imaging technique has proven to be a very robust and flexible method for the study of a wide range of systems with short signal lifetimes. As a pure phase-encoding technique, SPRITE is largely immune to image distortions generated by susceptibility variations, chemical shift and paramagnetic impurities, unlike clinical magnetic resonance imaging methods. It enables systems with transverse lifetimes as short as tens of microseconds to be successfully visualized. Our experimental results show that most sedimentary rocks have a single exponential transverse magnetization decay for T*2, which suggests that quantitative imaging of local fluid content can be easily obtained. Some examples of MRI techniques are represented that reveal internal sedimentary characteristics and heterogeneity. In addition, the application of quantitative MRI techniques to examine flow mechanisms in rock cores is outlined.